I remember EFB to ram used to run really slow in skyward sword with OGL, now it suddenly runs full speed. I did however, upgraded to a Skylake CPU. Is Skylake that much faster than Haswell for EFB to RAM or did someone messed with the efb to ram code.

I'm pretty sure Maxwell cards (GT 750, GTX 750 Ti, GTX 8xx, GTX 9xx) compress stuff before sending it through the memory bus, so they perform as if they had a higher memory bandwidth than they actually do. AMD have some cards which do this, too, but I'm pretty sure they deemed it unnecessary for their HBM cards (the Fury series).

OS: Windows 10 64 bit Professional
CPU: Intel i5 4670K @3.4GHz... for now @4.6GHz with a quick and dirty (yet stable) OC. May get faster in a bit before the end of time.
RAM: 16GB (Down from 24 GB after some was given to siblings)
GPU: Radeon Vega 56